Direct wind technology has been used to manufacture Superconducting magnets for various accelerator projects. Direct wire technology has relied on having each conductor wind being coated with a thermally activated special adhesive such as Bondall 16-H, which sets almost immediately. See column 5, lines 5-11 of U.S. Pat. No. 5,547,532 to Wernersbach, Jr. et al. Special end effectors are then used to position and bond the coated wires together by melting or setting the adhesive. The melting and setting has been done by thermal heating with small electrical heaters or by ultrasonic heating. In order to assemble layers of the conductor stacks together, the adhesive requires thermoplastic properties where the adhesive of the wire in the lower layer melts again and bonds to the adhesive in the wire layer above. The process of coating the conductor with appropriate adhesive is rather complex and requires large towers which are traversed several times to build up the required thickness of the adhesive layer which has to be 5 to 10% of the conductor diameter depending on the chosen spacing of conductors. Since it becomes increasingly difficult and expensive to build up thicker layers of adhesive, the Direct wind technology is limited to small conductor diameters of typically 0.5 mm and the design flexibility of choosing larger gaps between conductors is rather limited. The problem is compounded by the fact that gaps of varying size exist between conductors in a typical coil. Still another problem with the pre-coating process is that the wire guide tube of the end effector can clog up with the heated adhesive. The required pre-coating of the wire compromises the advantages of the Direct wind technology, in particular the important prospect of cost effective and rapid prototype manufacturing.
Various other patents besides Wernersbach, Jr. et al. have attempted to assemble wire coils but also fail to overcome the problems presented above. See for example U.S. Pat. Nos. 4,668,544 to Takahashi; 5,160,568 to Gruber; 5,213,646 to Zsolnay et al.; 5,426,407 to Van Den Berg et al.; and 5,514,308 to Cohen et al.
One of the unique features of the Direct wind technology is its ability to assemble 3-dimensional conductor patterns with high precision. In practice however it has been observed that the first layer which is put on a curved support structure like a cylinder or saddle has the tendency to slip on that surface and part of the intrinsic positioning accuracy given by the wire placement machine and the end effector is lost due to the conductor slippage. The field uniformity of a magnet, in particular a superconducting magnet, is controlled by accurate conductor placement, and any conductor slippage during the magnet assembly process compromises the field uniformity. In early versions of the Direct wind technique the conductor is wound and bonded to a flat substrate and this substrate is then wrapped around a support tube if the coil has a cylindrical shape. This technique does not work for coils with more than 3 layers because the wrapped pattern requires more wire length in the outer layers where the radius of the wrapped cylinder is larger. Furthermore, the precision of the wrapped pattern cannot compete with the direct winding on a 3-dimensional support structure. Thus, there is a loss of wind placement accuracy in the traditional direct wire process due to wind slippage, wire movements on the support structure, or wrapping a 2 dimensional pattern around a tube.